\begin{equation}
	\ell_{j}(x): = \prod_{0 \leq m \leq k; \quad m \neq j}\frac{x - x_m}{x_j - x_m} = \frac {x - x_0}{x_j - x_0}\cdots \frac {x - x_{j - 1}}{x_j - x_{j - 1}}\frac {x - x_{j + 1}}{x_j - x_{j + 1}}\cdots \frac {x - x_k}{x_j - x_k}
\end{equation}
